1. Field of the Invention
The present invention relates to an apparatus for measuring moisture within a specimen by exposing near-infrared radiation thereto, and more particularly to a compact desk-top type infrared radiation moisture measuring apparatus in which unusually large errors due to variations in the amount of lights reflected from a specimen may be eliminated.
2. Prior Art
Conventionally, a so-called infrared radiation moisture meter has been known as an apparatus for measuring moisture by use of near-infrared radiation where a measurement light in the near-infrared radiation region that is easily absorbed by water is exposed to the specimen, and the moisture within the specimen is measured on the basis of the light reflected from the specimen. With this type of moisture meter, a reference light that is not absorbed by water appreciably is exposed to the specimen just as is in the measurement light, and the amounts of the reflected measurement light is compared with that of the reflected reference light to compensate for measurement errors due to difference in the colors or compounds of the specimen.
This type of moisture measuring apparatus finds its application in determining moisture rate within tobacco leaves being carried on the conveyor of a tobacco manufacturing process for controlling moisture content in the tobacco leaves. A compact desk-top type infrared radiation moisture measuring apparatus that operates on the above-mentioned principle has been proposed for facilitating measurement of the moisture in various specimens in a laboratory.
However, unlike drying method, this type of apparatus indirectly measures the moisture in terms of the amount of the reflected lights exposed to the specimen; therefore the apparatus suffers from a problem that variations of the moisture depending on light-exposed portions or the top shape of the specimen, e.g., the surface shape of powder-like specimens, is a source of measurement errors. This measurement error causes little or no effect in controlling the moisture in a large quantity of the tobacco leaves, for example, in the tobacco manufacturing process but is a serious problem in measuring the moisture of a specimen of a small quantity, such as measurement of moisture using the desk-top infrared radiation moisture measuring apparatus where the moisture in a small amount of specimen is determined through a limited number of measurements.